The objective of this workstatement is to use gene expression arrays to examine for changes in expression following treatment with at least 6 chemopreventive agents in each of at least two human preinvasive cell culture systems. The proposed expression system allows for rapid readout of the proposed RNA levels employing a standardized software package. The preinvasive cell culture systems are derived from mammary. In addition NCI is suppling an additional 40 cell samples on which such an RNA analyses can be performed. These samples are from human cells or cell cultures. A preliminary toxicity in the cell culture determines the doses to be used. The RNA expression levels are determined from duplicate cell cultures, at each dose, exposed to control medium and three doses of two different chemopreventives for a period of at least three days. The specific chemopreventives to be employed will be retinoids, DFMO, antiestrogens , antiandrogens or NSAIDS. The agent to employed will depend on the specific cell line used. These studies should determine a) the reproducibility of the assay, b) whether their are distinctly different RNA patterns for following exposure of human preinvasive cells to different classes of chemopreventive agents, and (c) whether a dose effect can be seen. Following completion and analysis of these initial studies further studies will be undertaken. Five different agents in duplicate at three different time points (4 hours, 24 hours and 96 hours after the addition of the chemopreventive agents) employing 3 different doses of each agents is being assayed.